2008 REED’s East Coast Edition - Weather
direction in response to seasonal and cli- ence in temperature between a prevailing air
matic influences. Day-to-day observations of mass and the air immediately above a current.
ocean currents often show speeds and direc- Fog forms off the New England coast when
tion that depart markedly from yearly aver- the warm, moist air associated with the Gulf
ages. These variations are most frequently Stream meets the much colder water north of
caused by changes in wind strength and the Stream. Likewise, low-pressure systems
direction. In addition, phenomena such as often form or intensify off the North Carolina
volcanic eruptions, El Niño events and sun- coast when the warm air over the nearby Gulf
spots all affect global heat distribution and, Stream meets the cooler air over the land.
ultimately, the movement of ocean currents.
The Gulf Stream
Major ocean currents should not be
confused with the many local coastal and
The Gulf Stream tracks northward along
inshore currents that are affected by tides,
the southeast coast, then northeastward to-
seasonal wind patterns, temperature differ-
ward Cape Hatteras, where it begins to curve
entials, coastal configuration, and land-water
east, becoming broader and slower. After
runoff. Coastal currents can affect the depar-
passing the Grand Banks off Newfoundland,
ture and arrival phases of your voyage. Here
it turns more toward the north and becomes
are a few facts about the planet’s primary
a broad drift current flowing across the
ocean currents:
North Atlantic.
• Major ocean currents are located between
When the Gulf Stream encounters the cold
the equator and 50 degrees north and
water of the Labrador Current, principally in
south latitude.
the vicinity of the Grand Banks, there is little
• These currents turn clockwise in the
mixing of the waters. Instead, the junction
Northern Hemisphere and counterclock-
is marked by a sharp change in temperature.
wise in the Southern Hemisphere.
The line or surface along which this occurs is
• In the Northern Hemisphere, currents
called “the cold wall.” When the warm Gulf
on the western side of ocean basins are
Stream water encounters cold air, evapora-
stronger than those on the eastern side.
tion is so rapid that the rising vapor may be
• Currents are categorized as either warm
visible as frost smoke.
or cold in comparison with the water
The maximum current off Florida ranges
outside their flow.
from about 2 to 4 knots. It decreases fur-
• Eddies of warm water associated with ma-
ther after the current passes Cape Hatteras
jor currents normally circulate clockwise
and meanders into northerly and southerly
in the Northern Hemisphere; cold eddies
ridges and troughs. As it meanders, its ex-
circulate counterclockwise. The reverse
tent does not always coincide with the area
applies in the Southern Hemisphere.
of warm, blue water. A recirculation region
Effects of Currents on Vessels: When
exists adjacent to and southeast of the Gulf
planning a passage, you should consider the
Stream. In the recirculation region there is
potential effect of any major ocean current
a counter current, opposite to that in the
you will encounter. A current can advance a
Gulf Stream and surface currents are much
vessel far along its intended track or can put
weaker, generally less than half a knot.
it seriously off course. Electronic charts and
Eddies & Patterns: The Gulf Stream’s most
GPS navigation make plotting or compen-
significant changes in direction seem to oc-
sating for a current easier than ever before.
cur as it begins flowing eastward, south of
Consider ocean currents in relationship to
New England.
anticipated weather. Wind that blows con-
There the Stream develops meanders—
trary to a current can produce abnormally
northward and southward loops in the cur-
high seas. A northerly wind against the
rent. These loops tend to move parallel with
Atlantic Ocean’s Gulf Stream, for instance,
the general direction of the Stream. Occa-
can produce seas 50 percent higher than if
sionally, these loops or meanders will pinch
the wind were not opposing the current.
off at the base, leaving a separate, circular-
Ocean currents can have a strong effect on
flowing ring of current known as an eddy.
the weather. Fog and low-pressure systems
Eddies which develop north of the main
may form when there is a significant differ-
body of the Stream are known as warm
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